Particulate zinc alloys

ABSTRACT

Zinc base particulate alloys exhibiting both high tensile strength and high ductility, and containing titanium uniformly dispersed throughout the zinc matrix, with the zinc alloy having the form of small particles prepared by a melt-fragmentation process, such as atomisation or shotting. The zinc alloy may also contain small amounts of other metals, such as chromium, nickel and aluminum.

United States Patent [191 Radtke et al.

[451 Aug. 21, 1973 PARTICULATE ZINC ALLOYS Inventors: Schrade F. Radtke,New Canaan,

Conn.; John A. Lund, Vancouver, British Columbia, Canada InternationalLead Zinc Research Organization, Inc., New York, NY.

Filed: Mar. 9, 1971 Appl. No.: 122,509

Related US. Application Data Continuation of Ser. No. 651,676, July 7,1967, abandoned.

Assignee:

US. Cl. 75/178 R, 75/178 A Int. Cl. C22c 17/00 Field of Search 75/178 R,178 A References Cited UNITED STATES PATENTS 9/1970 Foerster 75/178 APrimary Examiner-L. Dewayne Rutledge Assistant Examiner-E. L. WeiseAttorney-Brumbaugh, Graves, Donohue & Raymond [5 7] ABSTRACT Zinc baseparticulate alloys exhibiting both high tensile strength and highductility, and containing titanium 4 Claims, No Drawings PARTICULATEZINC ALLOYS This is a continuation of application Ser. No. 651,676,filed July 7, 1967, now abandoned.

This invention relates to zinc base alloys, and more particularly tozinc base alloys in particulate form containing titanium and othermetals, and a process for preparing them.

For many years practitioners in the art have attempted to prepare zincbase alloys exhibiting properties of both high tensile strength forcasting and high ductility for forming and drawing. It is known thattitanium forms alloys with zinc which exhibit high tensile strength forcasting purposes. It is also known that zinc may be alloyed withtitanium in such a manner as to form an alloy with high ductilitycapable of being easily drawn and formed. No method is known, however,to prepare a zinc-titanium alloy exhibiting both properties together.

The known methods of alloying zinc with titanium have required theinclusion of copper in the alloy to create a satisfactory dispersion ofthe titanium in the zinc matrix. Heretofore, those zinc-titanium alloysprepared without copper have had notably poor yield strength andductility.

Furthermore, known zinc-titanium alloys exhibit low creep resistance,and the matrix grain coarsens noticeably when the alloy is heated. Thecoarsening of the grain results in lowered ductility and tensilestrength. in addition, known zinc-titanium alloys have a high transitiontemperature, below which the deformation behavior of the alloy changesfrom ductile to brittle. The relatively large grain size of the knownzinc-titanium alloys causes the alloys to become rapidly brittle as thetemperature is lowered.

It is therefore an object of this invention to prepare a particulatezinc base alloy with titanium which exhibits high tensile and yieldstrengths and at the same time a high degree of ductility, and whichdoes not require the presence of copper in the alloy. It is also anobject of this invention to prepare a zinc base alloy containingtitanium and other metal additives, such as chromium, nickel andaluminum, which exhibits both high ductility and high tensile strength.It is a further objective of this invention to prepare zinc base alloyswith titanium and other metals, having a fine matrix grain andexhibiting the properties of high creep resistance, high resistance tograin coarsening when subjected to heat treatments, and having a notablylow transition temperature from ductile to brittle deformation behavior.

.A particulate zinc-titanium alloy having the desired properties may beprepared according to the invention by the following process: An amountof zinc is heated to its molten state and approximately 0.02 to 1.5percent by weight of titanium is added to the molten zinc. The resultingalloy melt is fragmented and rendered particulate by any appropriatemelt-fragmentation process, such as atomisation or shotting. The averageparticle size should be less than 0.1 inch in diameter and is preferablyless than 0.01 inch in diameter. For preparing a coarser particulatematerial of average particle size 0.] inch or greater approximately 0.02to 0.5 percent by weight of titanium should be added to the molten zincand the resultant melt fragmented.

in particulate material produced by fragmenting an alloy melt to grainsize of the matrix phase is inherently fine because of the rapidsolidification of the melt fragments. Beyond its limit of solidsolubility in zinc, titanium is present as very fine grains of azinc-titanium intermetallic compound dispersed in the matrix phase. Thefine grain intermetallic compound tends to restrict or to prevent thegrowth of the grains in the matrix phase during subsequent mechanical orthermal treatment of the alloy particles. Since a fine matrix grain sizeis associated with high alloy ductility, the presence of titanium inexcess of its solid solubility in zinc gives particulate zinc alloys ahigh and relatively stable ductility. In addition, products made fromsuch particulate alloys by known processes such as compaction, rolling,

, extrusion or combinations thereof, will also possess these desirableproperties;

At higher levels of titanium content in these zinc alloys, the amount ofthe intermetallic compound is sufficient to provide strengthening of thematrix phase at ambient, elevated, and sub-normal temperatures. Thestrengthening effect of the intermetallic compound is greater for finerdispersions of the compound. A finer dispersion is assured by very rapidsolidification of the alloy, as in making particulate material by knownmeltfragmentation processes. The particulate alloys, or products madefrom them by suitable known compaction and working processes, therebyhave high strength properties. The advantage of the alloys describedherein is that the dispersion of zinc-titanium compound is extremelysensitive to rate of solidification. It is therefore possible with thesealloys to obtain very appreciable amounts of strengthening inparticulate forms, or in forms derived from the particles produced bymelt-fragmentation.

The combination of high yield strength, high creep strength, and highductility demonstrated by the products of this invention is greatlyimproved over that previously obtainable from known zinc alloys in castform or exhibited by known conventional wrought zinc alloys.

Other metals may be added to the zinc-titanium alloys to enhance theproperties of the alloy as recited above and to improve othercharacteristics. In particular, chromium, nickel or aluminum may beadvantageously added to the alloy, although other metals ma be employed.1

Preparation of a particulate zinc-titanium-chromium alloy may beundertaken by adding approximately 0.02 to 1.5 percent by weight oftitanium plus 0.01 to 0.5 percent by weight of chromium to molten zinc.The resulting liquid solution of chromium and titanium in zinc is thenmelt-fragmented by appropriate means to yield a solid powder. Inaddition to the desirable characteristics of high strength and highductility, the combination of titanium and chromium in a zinc-alloy,above their solid'solubility limits in zinc gives dispersions of finegrains of binary and/or ternary intermetallic compounds which are veryresistant to coarsening when the particulate forms, or forms derivedfrom the particles, are heated. I

Nickel may be added to the zinc-titanium alloy. A particulatezinc-titanium-nickel alloy is prepared according to the invention byadding approximately 0.02 to 1.5 percent by weight of titanium plus 0.1to 3.5 percent by weight of nickel to molten zinc. The resultant liquidsolution is then melt-fragmented to form a solid powder.

The zinc-titanium-nickel alloy exhibits properties set forth for boththe zinc-titanium alloy and the zinc-- titanium-chromium alloy. inaddition, the high ductility and creep resistance, particularly creepresistance at elevated temperature, are maintained at the same levelsafter thermal treatments. The reason is that the binary and/or ternaryintermetallic compounds, formed when both nickel and titanium arepresent in the zinc alloy, above their limits of solid solubility inzinc, appear to have a very strong tendency to remain at matrix grainboundaries even at temperatures high enough to cause substantialcoarsening of the compound grains.

It is also within the contemplation of this invention to prepareparticulate alloys of zinc, titanium and aluminum. These are preparedaccording to the invention by adding approximately 0.2 to 1.5 percent byweight titanium and 0.3 to 6.0 percent by weight aluminum to moltenzinc. The resultant liquid solution is meltfragmented to yield a solidpowder which has the same properties as the zinc-titanium-chromiumalloys described above, including the binary and/or ternaryintermetallic compounds.

The presence of aluminum in combination with titanium in particulatezinc alloys makes it possible to alter the mechanical and creepresistant properties of the alloy by heat treatment. A particulatezinc-titaniumaluminum alloy has a very high ductility which is desirablefor purposes of drawing and forming. The high ductility can bemaintained in other forms obtained from the particulate form. An objectwhich is readily fabricated from this particulte alloy in its ductilecondition can then be strengthened appreciably by a final heattreatment. The heat treatment is particularly beneficial in respect tocontrol of creep strength.

A transition from ductile to brittle deformation behavior is observed inzinc and all zinc alloys at low temperatures. The temperature at whichbrittle behavior begins is lower for the finer grain sizes, and dependsheavily on composition factors. An advantage of the present invention isthat material wrought from particulate zinc-aluminum-titanium alloys hasa notably low transition temperature.

The following examples are intended to illustrate the invention only andare not to be considered as defining the scope of the invention:

EXAMPLE I An alloy containing 0.80 weight per cent titanium was preparedby adding an appropriate amount of titanium to molten zinc. Theresultant liquid solution of titanium in zinc was air-atomised to obtaina solid powder with a wide range of particle sizes. This powder wasscreened to obtain a mesh fraction passing through a No. 200 TylerScreen, but remaining on a No. 325 Tyler Screen. The 200 X 325 fractionwas compacted isostatically in rubber bags to obtain cylindrical billetsof roughly 1 inch diameter by 3 inches length. The porous billets werethen forward-extruded at 400F to obtain dense wire of approximately 0.15inches diameter. The extruded wire was cooled to ambient temperature(about 70F) and later tested. Tension tests at 70F and at a strain rateof '1 inch per minute gave the following results:

Yield strength (0.2% offset) 43,100 p.s.i.

Ultimate tensile strength 46,600 p.s.i.

Elongation to fracture (in 1 inch) 22.6% The combination of yieldstrength and elongation (ductility) represented by these results is muchimproved over that previously available from known zinc alloys in castforms, or in forms derived from casting. This reflects thecharacteristic structure of these particulate alloys.

The creep resistance of the particulate zinc 0.80 weight per centtitanium alloy was also studied. At 77F, extruded wire made from theparticulate alloy crept at a steady-state rate of 0.5 per cent per yearafter 3,500 hours under load at a stress of 25,000 p.s.i. This is muchhigher creep strength than is exhibited by known conventional wroughtzinc alloys.

EXAMPLE II An alloy containing 0.21 weight per cent titanium and 0.07weight per cent chromium in zinc, was prepared by adding appropriateamounts of titanium and chromium to molten zinc. The resulting liquidsolution of chromium and titanium in zinc was air-atomised to yieldsolid powder. A plus 200 mesh, minus 100 mesh (Tyler) screened fractionof the atomised powder was obtained, and was isostatically compacted tozinc billets roughly 1 inch diameter by 3 inches length. The porousbillets were extruded at 4l0-430F, to yield 0.15 inch diameter densewire. This wire was subsequently tested with the following results:Tensile properties (at F and 1.0 inch per inch per minute) I Yieldstrength (0.2% offset) 63,000 64,400 psi.

Ultimate tensile strength 67,000 p.s.i.

Elongation (in one inch) 8.5 to 9.5%

Creep properties (at 77F) I At 20,000 p.s.i., crept at 0.21 percent peryr. after 3,390 hrs.

At 30,000 p.s.i., crept at 0.76 percent per yr. after 3,280 hrs. Thiscombination of high tensile and creep resistant properties isappreciably better than that of known alloys conventionally processed towrought material, and is attributable to the characteristic structure ofthese particulate alloys.

EXAMPLE Ill An alloy containing 0.22 weight per cent titanium and 0.6percent nickel in zinc was prepared by making appropriate additions tomolten zinc. The resultant liquid solution was air-atomised to yieldsolid powder. A minus 200 plus 325 Tyler mesh fraction of the powder wascompacted isostatically to give a billet of about 1 inch diameter and 3inches length. The porous billet was forward-extruded at 350F to obtaindense wire of 0.15 inches diameter. As-extruded, the properties of thewire were as follows:

Tensile properties at 70F and l inch/inch/min.

Yield Stress (0.2% offset) 25,800 p.s.i.

Ultimate tensile strength 31,100 p.s.i.

Elongation (in 1 inch) 47.5%

Creep properties at 205F. Steady state creep rate, when loaded at 6,000p.s.i., was 0.25 percent per year after 3,560 hrs. Creep properties at77F. Steady state creep rate, at 12,000 p.s.i., was 0.05 percent peryear after 3,550 hrs. This combination of high creep resistance and hightensile ductility is unusual, and is attributable to the characteristicstructure of this particulate alloy.

EXAMPLE lV An alloy containing 0.92 weight per cent aluminum and 0.12weight per cent titanium in zinc was prepared by making appropriateadditions to molten zinc. The resultant liquid solution was air-atomisedto yield solid powder. A minus 200, plus 325 Tyler mesh fraction of thepowder was compacted isostatically to give a billet of about 1 inchdiameter and 3 inches length. This porous billet was forward-extruded at400F to obtain dense wire of 0.15 inches diameter. As extruded, the wirehad the following tensile properties at 70F and 1 inch per inch perminute:

Yield stress (0.2% offset) 7,200 p.s.i.

Ultimate tensile strength 9,600 p.s.i.

Elongation (in 1 inch) 208% These properties reveal the excellentformability of the as-extruded material from particulate alloys,especially at low strain rates. The properties are derived from thecharacteristic structure of these particulate alloys.

The as-extruded material above was heat-treated by holding it for 30minutes at 660F, and then air-cooling it. This gave a sharp increase instrength properties at low strain rates, with a corresponding decreasein ductility. However, the strength at higher strain rates wasrelatively unaffected. Thus, the 660F heat-treatment resulted in muchless strain-rate sensitivity of strength. For 660F treated material, theyield stress (0.2 percent offset) varied with strain rate as follows:

0.01 per min. 24,000 p.s.i.

1.0 per min. 28,000 p.s.i.

The as-extruded material also exhibited more than 1O per cent tensileelongation to fracture when tested at We claim:

1. A zinc based particulate alloy having a fine grain matrix, containingapproximately 0.02 to 1.5 percent by weight of titanium and the balancemainly zinc, with fine grains of zinc-titanium intermetallic compoundpresent in said alloy above the solid solubility of tita nium in zinc,being dispersed substantially uniformly throughout said fine grain zincmatrix, said alloy having the form of particles with a maximum averagediameter of less than 0.1 inch and exhibiting high ductility and hightensile strength, said alloy consisting essentially of zinc, titaniumand 0.1 to 3.5 percent by weight nickel, with said titanium and nickelbeing dispersed as fine grain intermetallic compound selected from thegroup consisting of binary and ternary intermetallic compoundscontaining titanium and nickel above the limits of their solidsolubility in zinc, substantially uniformly throughout said fine grainzinc matrix.

2. A zinc based particulate alloy having a fine grain matrix, containingapproximately 0.02 to 1.5 percent by weight of titanium and the balancemainly zinc, with fine grains of zinc-titanium intermetallic compoundpresent in said alloy above the solid solubility of titanium in zinc,being dispersed substantially uniformly throughout said fine grain zincmatrix, said alloy having the form of particles with a maximum averagediameter of less than 0.1 inch and exhibiting high ductility and hightensile strength, said alloy consisting essentially of zinc, titaniumand 0.3 to 6.0 percent by weight alunminum, with said titanium andaluminum being dispersed as fine grain intermetallic compound selectedfrom the group consisting of binary and ternary intermetallic compoundscontaining titanium and aluminum above the limits of their solidsolubility in zinc, substantially uniformly throughout said fine grainzinc matrix.

3. A zinc base alloy having a fine grain zinc matrix and capable ofbeing wrought, comprising compacted particles of zinc-titanium alloy,said alloy containing approximately 0.02 to 1.5 percent by weight oftitanium and the balance mainly zinc, with fine grains of zinc-titaniumintermetallic compound present in said alloy above the solid solubilityof titanium in zinc, being dispersed substantially uniformly throughoutsaid fine grain zinc matrix, said alloy consisting essentially of zinc,titanium and 0.1 to 3.5 percent by weight of nickel, with said titaniumand said nickel being dis persed as fine grain intermetallic compoundselected from the group consisting of binary and ternary intermetalliccompounds containing titanium and nickel above the limits of the solidsolubility in zinc, substantially uniformly throughout said fine grainzinc matrix.

4. A zinc base alloy having a fine grain zinc matrix and capable ofbeing wrought, comprising compacted particles of zinc-titanium alloy,said alloy containing approximately 0.02 to 1.5 percent by weight oftitanium and the balance mainly zinc, with fine grains of zinc-titaniumintermetallic compound present in said alloy above the solid solubilityof titanium in zinc, being dispersed substantially uniformly throughoutsaid fine grain zinc matrix, said alloy consisting essentially of zinc,titanium and 0.3 to 6.0 percent by weight of aluminum, with saidtitanium and said aluminum being dispersed as fine grain intermetalliccompound selected from the group consisting of binary and ternaryintermetallic compounds containing titanium and aluminum above thelimits of the solid solubility in zinc, substantially uniformlythroughout said fine grain zinc matrix. =0:

2. A zinc based particulate alloy having a fine grain matrix, containingapproximately 0.02 to 1.5 percent by weight of titanium and the balancemainly zinc, with fine grains of zinc-titanium intermetallic compoundpresent in said alloy above the solid solubility of titanium in zinc,being dispersed substantially uniformly throughout said fine grain zincmatrix, said alloy having the form of particles with a maximum averagediameter of less than 0.1 inch and exhibiting high ductility and hightensile strength, said alloy consisting essentially of zinc, titaniumand 0.3 to 6.0 percent by weight alunminum, with said titanium andaluminum being dispersed as fine grain intermetallic compound selectedfrom the group consisting of binary and ternary intermetallic compoundscontaining titanium and aluminum above the limits of their solidsolubility in zinc, substantially uniformly throughout said fine grainzinc matrix.
 3. A zinc base alloy having a fine grain zinc matrix andcapable of being wrought, comprising compacted particles ofzinc-titanium alloy, said alloy containing approximately 0.02 to 1.5percent by weight of titanium and the balance mainly zinc, with finegrains of zinc-titanium intermetallic compound present in said alloyabove the solid solubility of titanium in zinc, being dispersedsubstantially uniformly throughout said fine grain zinc matrix, saidalloy consisting essentially of zinc, titanium and 0.1 to 3.5 percent byweight of nickel, with said titanium and said nickel being dispersed asfine grain intermetallic compound selected from the group consisting ofbinary and ternary intermetallic compounds containing titanium andnickel above the limits of the solid solubility in zinc, substantiallyuniformly throughout said fine grain zinc matrix.
 4. A zinc base alloyhaving a fine grain zinc matrix and capable of being wrought, comprisingcompacted particles of zinc-titanium alloy, said alloy containingapproximately 0.02 to 1.5 percent by weight of titanium and the balancemainly zinc, with fine grains of zinc-titanium intermetallic compoundpresent in said alloy above the solid solubility of titanium in zinc,being dispersed substantially uniformly throughout said fine grain zincmatrix, said alloy consisting essentially of zinc, titanium and 0.3 to6.0 percent by weight of aluminum, with said titanium and said aluminumbeing dispersed as fine grain intermetallic compound selected from thegroup consisting of binary and ternary intermetallic compoundscontaining titanium and aluminum above the limits of the solidsolubility in zinc, substantially uniformly throughout said fine grainzinc matrix.